The invention relates to an electroslag remelting plant including an ingot mold for forming a block from the material of at least one consumable electrode, including a rack having at least one vertically driven electrode rod for the advance of at least one consumable electrode and including a hood disposed above of the ingot mold which has at least one concentric aperture toward the respective electrode axis.
Such a remelting plant is known from the German DE-AS No. 20 31 708, to which U.S. Pat. No. 3,729,307 corresponds. The hood described therein is used to reduce the radiation loss and for this purpose it is coated with mineral heat insulator. In this achievement of the object it is not the electrode rod but the electrode itself which passed through the hood. Since consumable electrodes of this kind commonly have an irregularly formed surface it is necessary that the aperture in the hood be correspondingly large in dimension. Since the hood is placed onto the top edge of the ingot mold, insulated spacers are inserted so as to avoid a short-circuit; this causes a chimney effect, i.e. surrounding air is sucked in through the gap at the bottom to escape again through the annular gap between the hood and the electrode. This gas circulation leads to significant problems which will be dealt with hereinafter.
In the remelting process the molten slag, which is at a high temperature, assumes in a way the function of a heating resistor. The metal of the consumable electrode immersing into the liquid slag is passed through the slag in the form of drops and gathers underneath to form a melt which solidifies at its lowest phase interface into a block or ingot. The heat removal necessary for the solidification is usually carried out by means of a cooling agent (water) flowing through the ingot mold unit. The slag which can have different compositions depending on the impurities to be removed and the metals used is essential to metallurgic purification process. Slag compositions are known in great numbers.
The remelting process described produces gases which not escape into the atmosphere but must be exhausted. In several cases it is also advantageous to pass an oxygen-containing gas over the slag to burn a part of the sulfur which is gathering in the liquid melt. On the other hand, during this process moisture from the surrounding air must be avoided from entering in the melt to be reduced to hydrogen. The hydrogen would be absorbed by the forming block.
In order to also eliminate the effects of atmospheric moisture known hoods were provided with a dry air supply which, however, met the requirements in a less than satisfactory way. In this process large amounts of dry air are required which, in turn, involves high investments costs for the plant to generate this dry air. Since this process also involves large amounts of waste air this calls for additional investment costs for the necessary exhaust gas purification systems.
Initial experiments with electroslag remelting processes included attempts in vacuum arc furnaces which by manufacture can be hermetically closed. However, the vacuum-tight design of these furnaces extremely expensive and labor-intensive, moreover, the bell-shaped upper parts of these furnaces hamper the process control. However, the vacuum-tight design of these furnaces involves an extremely high amount of labor and cost and, moreover, the bell-like upper part of these furnaces hampers process operation. Complicated lifting devices must hence be provided for the charging of such furnaces which again tremendously increases the overall investment costs for such remelting plants. Hence, electroslag remelting in vacuum arc furnaces did not prevail on the market for large-scale industrial use.